1. Field of the Invention
This invention relates to a robot apparatus having a plurality of joint degrees of freedom, and particularly to a robot apparatus which includes a moving mechanism such as movable legs.
More particularly, the present invention relates to a robot apparatus which autonomously moves on the ground to perform positive and various physical interactions with a human being or an object, and more specifically to a robot apparatus which grasps a contacting state with the external field or a situation in which a force acts when the robot apparatus performs a physical interaction with a human being or an object.
2. Description of the Related Art
Research and development regarding the structure or stabilized walking control of a legged mobile robot have proceeded recently and also the expectation for practical use of a legged mobile robot is increasing. The legged mobile robot is less stable and more difficult in posture control and walking control than a crawler type robot. However, the legged mobile robot is superior in that flexible walking or running motion such as an ascending or descending motion on a staircase or a getting over motion of an obstacle can be implemented.
A robot in the past is applied principally to substitutive execution or supporting of various human works in industrial activities or production activities as represented by a six-axis manipulator. The robot in this instance presupposes that it acts in a structured environment such as a factory, and hence does not basically perform complicated physical interactions with a human being or an environment.
In contrast, attention is paid recently to an application of a robot as an application of the partner type, that is, an application to “symbiosis” with a human being or to “entertainment.” Such a robot as this type is desired to have an advanced ability to perform interactions with not only an object or an environment but also a human being.
A robot of the partner type is not fixed at a predetermined place like a six-axis manipulator but is normally formed as a mobile robot which autonomously moves to provide various services. A representative one of such partner type robots is a humanoid. A robot apparatus has been proposed and disclosed, for example, in Japanese Patent Laid-Open No. 2004-167676 (hereinafter referred to as Patent Document 1) which includes a moving mechanism and can produce a stable motion pattern for transition between grounding and non-grounding stages on the real time basis.
Most of partner type robots are not always used in such a manner that the posture is fixed. As occasion demands, a great variation in posture occurs with a robot of the type described such that it rolls about on the floor or falls down. Further, the robot interacts with an external world in various modes such as contact of the feet with the ground upon walking or handling of a tool with the hands. In other words, a portion of the robot at which the robot interacts with the external world is not limited particularly, and the robot contacts at an arbitrary portion of the machine body thereof with the external world.
In this manner, to a robot which performs positive and various physical interactions with a human being or an object, it is very important to grasp a contacting state with the external world or an acting situation of a force, that is, an external force applied to an arbitrary portion of the robot.
An external force acting upon a robot is detected normally by such a method that a force sensor represented by a six-axis force sensor or the like is disposed at a pertaining location so that an external force is detected directly by the force sensor.
A foot bottom grounding position detection apparatus for a leg type mobile robot is disclosed in Japanese Patent Laid-Open No. Hei 10-175180 (hereinafter referred to as Patent Document 2) wherein a six-axis force sensor is attached to an ankle and a point of action of a force and the acting force acting upon the bottom of the foot are detected. In the robot of Patent Document 2, a force sensor is provided at a portion above a foot platy portion of the robot. When the robot moves up and down on a staircase, a force component Fz in a Z direction perpendicular to the foot platy portion, a force component Fx in an X-axis direction which is a forward and backward direction, and a moment My around an axis in a Y-axis direction which is a leftward and rightward direction, are detected. Then, the position x of the center of the reaction force from the floor which acts on the sole is detected successively from the detected forces. Then, from the detected value of the force component Fz, the floor contacting starting time and the floor leaving finish time of the sole are detected, and the floor contacting starting grounding position and the floor leaving finish grounding position of the sole are determined from the position x determined within a range of time near the detection times.
However, with a robot of the type described, only a force applied to an end of the foot platy portion can be measured by the force sensor. Further, also where the robot has a plurality of points of action of force on the distal end side with respect to the force sensor, only a resultant force of the forces can be detected. Therefore, it is hard to specify the places of the individual points of action accurately, and determine the forces acting upon the individual points of action independently of each other.
Further, various proposals have been made for a method of specifying a portion of the body of a robot at which the body contacts with the external world by detecting a variation of electric signals from contact sensors or on/off switches attached to the overall area of the surface of the robot and made of a material whose resistance value or electrostatic capacitance varies in response to the pressure applied thereto. Such proposals are disclosed, for example, in “Development and Applications of Multivalued Touch Sensor That Cover Robots,” proceedings of the Robotics and Mechatronics Conference 1998 of The Japan Society of Mechanical Engineers, 1CI1-2, 1998 (hereinafter referred to as Non-Patent Document 1), “Development and Applications of Soft Tactile Sensor Made of Conductive,” proceedings of the 16th Annual Conference of the Robotics Society of Japan, pp.873 to 874, 1998 (hereinafter referred to as Non-Patent Document 2), or “A Full-Body Tactile Sensor Suit Using Electrically Conductive Fabric,” Journal of the Robotics Society of Japan, Vol. 16, No. 1, pp.80 to 86, 1998 (hereinafter referred to as Non-Patent Document 3).
However, a sensor of the type described is very low in accuracy when compared with general force sensors such as a six-axis force sensor and basically allows acquisition only of on/off information, that is, information regarding whether or not there exists contact with the external world. In other words, although the sensor of the type described can specify a contacting portion, it cannot detect a force acting upon the portion. Further, only if a detected value of the sensor is basically used as it is, information regarding the force acting upon the contacting portion cannot be obtained and the sensor value cannot be utilized for dynamic control of the entire robot.
Further, a more abundant contacting state with the external world can be obtained by raising the accuracy of force information which can be acquired by a distribution type tactile sensor as disclosed, for example, in “Tactile Sensing for Dexterous Hand,” Journal of the Robotics Society of Japan, Vol. 18, No. 6, pp.767 to 771, 2000 (hereinafter referred to as Non-Patent Document 4). However, according to the technical level at the point of time at which the present patent application is filed in Japan, a small-size sensor by which a frictional force and a normal reaction force can be acquired with a high degree of accuracy and which can be distributed to and disposed on the whole body of a robot has not been placed into practical use. Further, even if such a sensor as just described can be implemented in the future, since the amount of information of sensor values to be inputted is very great, there is the possibility that processing of such data or implementation of a data transmission method may be difficult or a result of increase of the cost of the system may be invited.